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CsF
PVK
CBP 2.3 eV
2.2 eV
2.2 eV
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TPBI
2.7 eV
Ir-1 2.91 eV
Ir-2 2.94 eV
Al
4.2 eV
ITO
Ir-1 4.96 eV
Ir-2 5.10 eV
PEDOT
4.9 eV
5.0 eV
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CBP 5.9 eV
5.8 eV
TPBI
6.7 eV
phorescence efficiency in an organic light-emitting device.
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J Appl Phys
Fig. 8. Energy level diagram for the materials used in devices.
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for displays. Adv Mater 2007;19:1675e88.
highlight the potential merits of this prominent class of iridium
dendrimers in simplifying high-efficiency OLED applications.
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4. Conclusion
An effective strategy for designing bipolar phosphorescent
dendrimers has been demonstrated for electrophosphorescent
devices. Introducing carbazolyl dendrons with excellent charge
transport properties at the edge of the emissive core and 1,2,4-
triazolyl unit moieties can significantly reduce the luminescence
self-quenching caused by intermolecular interactions. A peak LE
accompanied by high luminance was realized from a bilayer device.
Surface groups play an important role in controlling solubility and
intermolecular interactions, as indicated by the comparison of Ir-1
and Ir-2. We believe that this strategy is suitable for the design and
synthesis of novel solution-processable host-free phosphorescent
materials and devices.
[23] Ribierre JC, Ruseckas A, Knights K, Staton SV, Cumpstey N, Burn PL, et al.
Triplet exciton diffusion and phosphorescence quenching in iridium(III)-
centered dendrimers. Phys Rev Lett 2008;100:017402.
Acknowledgments
[24] Ulbricht C, Beyer B, Friebe C, Winter A, Schubert US. Recent developments in
the application of phosphorescent iridium(III) complex systems. Adv Mater
2009;21:4418e41.
[25] Chen LC, Ding JQ, Cheng YX, Xie ZY, Wang LX, Jing XB, et al. Bipolar hetero-
leptic green iridium dendrimers containing oligocarbazole and oxadiazole
dendrons for bright and efficient nondoped electrophosphorescent devices.
Chem Asian J 2011;6:1372e80.
[26] Lo SC, Anthopoulos TD, Namdas EB, Burn PL, Samuel IDW. Encapsulated cores:
host-free organic light-emitting diodes based on solution-processible elec-
trophosphorescent dendrimers. Adv Mater 2005;17:1945e8.
[27] Gambino S, Stevenson SG, Knights KA, Burn PL, Samuel IDW. Control of charge
transport in iridium(III) complex-cored carbazole dendrimers by generation
and structural modification. Adv Funct Mater 2009;19:317e23.
[28] Ding JQ, Wang B, Yue ZY, Yao B, Xie ZY, Cheng YX, et al. Bifunctional green
iridium dendrimers with a “self-host” feature for highly efficient nondoped
electrophosphorescent devices. Angew Chem Int Ed 2009;48:6664e6.
[29] Zhou GJ, Wong WY, Yao B, Xie ZY, Wang LX. Triphenylamine-dendronized
pure red iridium phosphors with superior OLED efficiency/color purity trade-
offs. Angew Chem Int Ed 2007;46:1149e51.
The authors sincerely appreciate the financial support given by
the National Natural Science Foundation of China (gs1) (50803008),
Natural Science Foundation of Hunan (gs2) (11B001, 2011RS4067),
Open Project Program of Key Laboratory of Environmentally
Friendly Chemistry & Applications of Ministry of Education (gs3)
(08hjyh02), Key Laboratory for Power Technology of Renewable
Energy Sources (gs4) (2011KFJJ006), the State Key Laboratory of
Luminescent Materials and Devices at South China University of
Technology (gs5) (2013-skllmd-08), China Postdoctoral Science
Foundation (gs6) (20100480946, 201104508).
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